Technical Abstract:
Efficient fermentation processes to produce ethanol from low-cost lignocellulosic biomass are sought to support the expansion of the biofuels industry. Stress-tolerant microorganisms are needed that are able to consume both hexose and pentose sugars and also withstand, survive, and function in the presence of stress factors common to fermentations of lignocellulose hydrolysates, including inhibitors such as furfural and hydroxymethylfurfural (HMF) and high concentrations of mixed sugars and ethanol. Data will be presented showing that nitrogen and carbon source composition and culture physiological state significantly impact the ability of Pichia stipitis to survive and detoxify furan inhibitors and to convert high xylose concentrations efficiently to ethanol. The utility of priming inocula with high xylose concentrations to induce faster fermentation rates in ethanol production fermentors and to eliminate diauxic lag during mixed sugar conversion was observed for P. stipitis NRRL Y-7124 as well as the more acid-tolerant Pachysolen tannophilus Y-2460. Implications of these findings on process-based strategies to produce a tolerant initial population and then to foster and maintain an efficient viable population during subsequent ethanol fermentation are considered.